The trend in automated machine tool systems is to require less and less operator intervention through the use of programmable machine tool controllers. The lack of direct continuous supervision by an operator increases the need for the use of various inspection devices and for means to ensure that such inspection devices are operating properly. One such inspection device is known as a touch probe. A touch probe generally includes a stylus that projects from one end of a housing, the stylus being moveable from its rest position when it touches an object. The probe is generally used like other tools in the system except that it is used to touch a workpiece surface and transmit information in response thereto back to the machine controller. Examples of touch probes are disclosed in U.S. Pat. Nos. 4,451,987 to Cusack and 4,509,266 to Cusack, both of which are assigned to the assignee of the present invention and are hereby incorporated by reference herein.
A particularly advantageous probe desihgn uses an infrared optical transmission of stylus position information to a remote receiver located within the general vicinity of the probe. One such probe transmission scheme is disclosed in the referenced U.S. Pat. No. 4,509,266 above. Unfortunately, the batteries used in probes of these types have somewhat limited useful lives. One approach used in the past to detect weak batteries is to light a lamp on the probe to indicate to the operator that the battery is low and needs to be replaced. This approach does, however, require an operator to be present in order to see that the low battery lamp has been activated. In addition, it can be sometimes difficult for the operator to see the lamp depending upon the lighting conditions in the area and the orientation of the probe.